Adhesive composition comprising eutectic metal alloy nanoparticles

ABSTRACT

Provided herein is conductive adhesive composition comprising at least one epoxy resin, at least one polymer chosen from polyvinyl phenols and polyvinyl butyrals, at least one melamine resin, a plurality of eutectic metal alloy nanoparticles, and at least one solvent. Also provided herein is an electronic device comprising a substrate, conductive features disposed on the substrate, a conductive electrical component disposed over the conductive features, and a conductive adhesive composition disposed between the conductive features and the conductive electrical component. Further disclosed herein are methods of making a conductive adhesive composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/713,893, filed Aug. 2, 2018, the disclosure of which is incorporatedherein by reference in its entirety.

DETAILED DESCRIPTION Field of the Disclosure

This disclosure relates generally to conductive adhesive compositionscomprising eutectic metal alloy nanoparticles, which, in embodiments,can be used in printed electronics. In embodiments, the adhesivecompositions herein can be jetted via inkjet, aerosol jet or other formsof jetting. In various embodiments, the conductive adhesive compositioncomprises at least one epoxy resin, at least one polymer chosen frompolyvinyl phenols and polyvinyl butyrals, at least one melamine resin, aplurality of eutectic metal alloy nanoparticles, and at least onesolvent. The conductive adhesive compositions disclosed herein can bedigitally printed by aerosol jet or inkjet printing and demonstrateexcellent adhesion strength, stability, and conductivity.

Background

Printed electronics, or the fabrication of electronic components usingliquid deposition techniques, has recently become of great interest.Such techniques may provide potentially low-cost alternatives toconventional mainstream amorphous silicon technologies for electronicapplications such as thin film transistors (TFTs), light-emitting diodes(LEDs), RFID tags, photovoltaics, printed memory, and the like. However,it has been a challenge to meet the conductivity, processing,morphology, and cost requirements for practical applications of printedelectronics using liquids.

Traditional processes for the fabrication of electronic circuit elementsrequire high temperature and pressure. Accordingly, conductive elementssuch as interconnects are typically formed on rigid surfaces, such assilicon. High temperatures and pressures limit the use of materialsavailable for printed electronics, which may, for example, use flexibleplastic substrates that melt at low temperatures, such as at about 150°C. or less.

Certain electrically conductive materials are known in the art for lowmelting temperatures and thus may be suitable for use on a wide range ofsubstrates, including flexible plastic substrates. For example, inkscomprising silver nanoparticles may have a high silver content, lowviscosity, and melting temperature less than or equal to about 145° C.Thus inks comprising silver nanoparticles are capable of formingconductive elements by bonding (sintering) the silver particle at lowtemperatures. Despite these benefits, however, silver nanoparticle inksoften do not adhere well to electronic components, thus limiting theiruse as interconnects.

Because it is desirable to have good adhesion between electroniccomponents of certain electronic devices, it is known to use ananisotropic conductive adhesive, commonly referred to as a Z-axisadhesive, to connect a conductive substrate, such as a circuit board, toa conventional electronic component. If the adhesive is conductiveacross the entire substrate, it will interfere with the traces byproviding additional paths of conductivity between the elements of thesubstrate. An anisotropic conductive adhesive provides electricalconductivity only in a direction perpendicular to the connected surfacesand not in a direction parallel to the surfaces. Thus, the anisotropicconductive adhesive does not create undesired additional paths ofconductivity between the elements of the substrate. Anisotropicconductive adhesives may include conductive particles dispersedthroughout an insulating adhesive matrix, such as an epoxy or a polymer.Known adhesives, however, are typically pastes, having a viscosity ofgreater than about 2500 cps. They are therefore unsuitable for use inliquid printing technologies, such as inkjet printing or aerosol jetprinting.

There is thus a need in the art for jettable conductive adhesivecompositions that enable printing and are suitable for fabricatinginterconnects as well as conductive features such as traces, electrodes,and the like on a variety of substrates, including flexible plasticsubstrates.

SUMMARY

Disclosed herein is a conductive adhesive composition comprising atleast one epoxy resin, at least one polymer chosen from polyvinylphenols and polyvinyl butyrals, at least one melamine resin, a pluralityof eutectic metal alloy nanoparticles, and at least one solvent. Incertain embodiments of the conductive adhesive composition, theplurality of eutectic metal alloy nanoparticles comprises Field's metal,and in certain embodiments, the plurality of eutectic metal alloynanoparticles further comprise at least one organoamine stabilizerselected from the group consisting of butylamine, octylamine,3-methoxypropylamine, pentaethylenehexamine,2,2-(ethylenedioxy)diethylamine, tetraethylenepentamine,triethylenetetramine, and diethylenetriamine.

In certain embodiments, the conductive adhesive composition has a solidscontent ranging from about 20% to about 80%, such as from about 30% toabout 50%, based on a total weight of the conductive adhesivecomposition, and in certain embodiments, the at least one solvent isselected from the group consisting of propylene glycol methyl etheracetate, di(propylene glycol) methyl ether acetate, (propyleneglycol)methyl ether, di(propylene glycol)methyl ether, methyl isobutylketone, diisobutyl ketone, 1-phenoxy-2-propanol. According to variousembodiments, the at least one melamine resin is selected from the groupconsisting of a methylated poly(melamine-co-formaldehyde), butylatedpoly(melamine-co-formaldehyde), isobutylatedpoly(melamine-co-formaldehyde), acrylatedpoly(melamine-co-formaldehyde), and methylated/butylatedpoly(melamine-co-formaldehyde), and in certain embodiments, thecomposition has a viscosity ranging from about 2 cps to less than about300 cps, such as less than about 100 cps, at a temperature of about 20°C. to about 30° C. In certain embodiments of the disclosure, the atleast one epoxy resin is selected from the group consisting of bisphenolA diglycidyl ether, bisphenol A propoxylate diglycidyl ether, glycidylepoxy resins, trimethylolpropane triglycidyl ether, neopentyl glycoldiglycidyl ether, poly(propylene glycol) diglycidyl ether,tris-(hydroxyl phenyl)-methane-based epoxy resins, and cycloaliphaticepoxides. According to certain embodiments, the conductive adhesivecomposition further comprises at least one adhesion promoter, and incertain embodiments, the at least one polymer is a polyvinyl polymerselected from the group consisting of poly(4-vinylphenol),poly-p-vinylphenol, poly(vinylphenol)/poly(methyl acrylate),poly(vinylphenol)/poly(methyl methacrylate), andpoly(4-vinylphenol)/poly(vinyl methyl ketone). In various embodiments ofthe disclosure, the conductive adhesive composition is jettable byinkjet or aerosol jet printing.

Also provided herein are methods of making a conductive adhesivecomposition comprising mixing at least one epoxy resin, at least onepolymer chosen from polyvinyl phenols and polyvinyl butyrals, at leastone melamine resin, and at least one solvent to create a mixture; andadding a plurality of eutectic metal alloy nanoparticles to the mixtureto create a conductive adhesive composition.

Also disclosed herein are electronic devices comprising a substrate,conductive features disposed on the substrate, a conductive electricalcomponent disposed over the conductive features, and a conductiveadhesive composition disposed between the conductive features and theconductive electrical component, wherein the conductive adhesivecomposition comprises at least one epoxy resin, at least one polymerchosen from polyvinyl phenols and polyvinyl butyrals, at least onemelamine resin, and a plurality of eutectic metal alloy nanoparticles.In certain embodiments of the methods disclosed herein, the plurality ofeutectic metal alloy nanoparticles comprise Field's metal alloy, and incertain embodiments, the conductive adhesive composition has a solidscontent ranging from about 20% to about 80%, based on a total weight ofthe conductive adhesive composition.

In certain embodiments of the electronic device, the substrate isselected from the group consisting of silicon, glass, plastics, sheets,fabrics, synethic papers, and mixtures thereof, and in certainembodiments, the substrate is selected from the group consisting ofpolyester, polycarbonate, polyimide sheets, polyethylene terephthalatesheets, polyethylene naphthalate sheets, and mixtures thereof. Incertain embodiments, the conductive features comprise an electricallyconductive element formed from a metal nanoparticle conductive inkcomposition, and in certain embodiments, the metal nanoparticleconductive ink composition is a silver nanoparticle conductive inkcomposition. In various embodiments of the disclosure the conductiveadhesive composition has a viscosity ranging from about 2 cps to about300 cps at a temperature of about 20° C. to about 30° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentteachings and together with the description, serve to explain theprinciples of the present teachings.

FIG. 1A is a schematic of an exemplary electrical device comprising aconductive adhesive composition as disclosed herein applied to thesurface of a conductive ink on a substrate.

FIG. 1B is a schematic of the application of a resistor to an exemplaryelectrical device comprising a conductive adhesive composition asdisclosed herein applied to the surface of a conductive ink on asubstrate.

FIG. 1C is a schematic of the application of a resistor to an exemplaryelectrical device comprising a conductive adhesive composition asdisclosed herein applied to the surface of a conductive ink on asubstrate after force has been applied to the resistor.

FIG. 2A is a schematic of the application of a resistor to an exemplaryelectrical device using an anisotropic conductive adhesive compositionas disclosed herein before the application of force to the resistorand/or curing of the anisotropic conductive adhesive composition.

FIG. 2B is a schematic of the application of a resistor to an exemplaryelectrical device using an anisotropic conductive adhesive compositionas disclosed herein before the application of force to the resistorand/or curing of the anisotropic conductive adhesive composition.

It should be noted that some details of the figures may have beensimplified and are shown to facilitate understanding of the embodimentsrather than to maintain strict structural accuracy, detail, and scale.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the presentdisclosure. The following description is merely exemplary.

Disclosed herein are conductive adhesive compositions having many uses,for example, for printed electronics. In certain embodiments, theconductive adhesive compositions disclosed herein comprise at least oneepoxy resin, at least one polymer chosen from polyvinyl phenols andpolyvinyl butyrals, at least one melamine resin, eutectic metal alloynanoparticles, and at least one solvent.

Conventional electronics use robust interconnects such as solder balls,wire-bonding, and anisotropic conductive pastes to attach microchips,capacitors, diodes, and other circuit elements. Conductive adhesives maybe used to attach conventional electronic silicon microchips to printedcircuitry. It is desirable for a conductive adhesive composition to havehigh conductivity, such as a conductivity of at least about 1000 S/cm,high adhesive strength, low curing temperature, such as less than about130° C., and a short curing time, such as less than about 2 hours. Mostconductive adhesives currently available are pastes (e.g., having aviscosity greater than about 2500 cps), which precludes jetting byaerosol jet or inkjet printing. Disclosed herein are jettable conductiveadhesive compositions having low viscosities (such as less than about2500 cps) and low curing temperatures for the printed electronicsindustry.

The conductive adhesive compositions disclosed herein may have anydesired viscosity. In certain embodiments, the viscosity ranges fromabout 2 cps to about 300 cps, such as from about 3 cps to about 200 cps,such as from about 3 cps to about 100 cps, from about 4 cps to about 50cps, from about 5 cps to about 20 cps, or from about 6 cps to about 10cps, as measured at about 20° C. to about 30° C. Viscosity can bemeasured by any suitable or desired method as known in the art, such aswith an Ares G2 Rheometer from TA Instruments. Viscosity data can beobtained, for example, at 25° C. on an Ares G2 Rheometer from TAInstruments using a 50 millimeter, 0.053 micron gap. The conductiveadhesive composition disclosed herein may have any feasible cure rate.In certain embodiments, the conductive adhesive composition may cure inless than about 24 hours, such as between about 30 minutes to about 12hours or between about 1 hour to 3 hours, such as in less than about 2hours.

In certain embodiments, the conductive adhesive compositions disclosedherein are anisotropic. As used herein, an anisotropic compositionrefers to a composition that is an electrical conductor in the z-axisand has low or no conductivity in the x-axis and the y-axis. As aresult, anisotropic compositions are also sometimes referred to asz-axis conducting compositions. The anisotropic compositions disclosedherein provide a matrix for electrically conducting elements that aredispersed in the composition that span the z-axis and provide theelectrical conduction through the composition. In certain embodiments,the conductive adhesive compositions disclosed herein do not contain anyadditional conductive elements other than the plurality of eutecticmetal alloy nanoparticles. For example, in certain embodiments, theconductive adhesive compositions disclosed herein are free of silverparticles, such as silver nanoparticles and silver flakes.

More particularly, the present disclosure provides a composition, whichmay be used in embodiments to form an adhesive between conventionalelectronic components such as resistors and printed conducted layers,constructed from various conductive compositions, such as metal inkcompositions, e.g., silver nanoparticle inks. The conductive adhesivecompositions disclosed herein can improve the adhesion between thesubstrates and conventional electronic components. Furthermore, theconductive adhesive compositions disclosed herein exhibit surprisinglyimproved dispersion, stability, conductivity, and adhesion. Accordingly,the resulting electrical devices formed from the present compositionshave surprisingly excellent conductive properties.

Epoxy Resins

The conductive adhesive compositions disclosed herein comprise at leastone epoxy resin. In certain embodiments of the conductive adhesivecompositions disclosed herein, the at least one epoxy resin is athermally-cured epoxy resin. In embodiments disclosed herein, there areeutectic metal alloy nanoparticles, such as Field's metal nanoparticles,evenly dispersed into a thermally-curable epoxy resin. The epoxy resinmay, for example, be cured at about 120° C. for about 2 hours, whichtraps the conductive pathways into place.

The epoxy resin component may be any type of epoxy resin, including anymaterial containing one or more reactive oxirane groups (also termedepoxy groups) as shown below.

Epoxy resins useful in embodiments disclosed herein may includearomatic, aliphatic or heterocyclic epoxy resins. The epoxies may bepure compounds or mixtures of compounds containing one, two or moreepoxy groups per molecule. In some embodiments, epoxy resins may alsoinclude reactive —OH groups.

In some embodiments, the conductive adhesive compositions includeglycidyl epoxy resins, such as glycidyl-ether epoxy resins,glycidyl-amine epoxy resins, and glycidyl-ester epoxy resins. Glycidylepoxy resins are commercially available or may be prepared via acondensation reaction of an appropriate dihydroxy compound andepichlorohydrin as is known in the art.

In some embodiments, the at least one epoxy resin may includenon-glycidyl epoxy resins, such as cycloaliphatic epoxy resins.Non-glycidyl epoxies are commercially available or may be formed byperoxidation of an olefinic double bond as known in the art.

Suitable epoxy resins may include those having aromatic moieties.Representative glycidyl-ether epoxy resins having aromatic moietiesinclude diglycidyl ethers of bisphenol-A (DGEBA), which may besynthesized by reacting bisphenol-A with epichlorohydrin in the presenceof a basic catalyst and which has the following structure.

In certain embodiments, x, the number of repeating units, ranges from 0to 25, such as from about 2 to about 20 or about 5 to about 15.

DGEBA resins are commercially available and are marketed under the tradedesignations Epon® 828, Epon® 1001, Epon® 1004, Epon® 2004, Epon® 1510,and Epon® 1310 from Hexion, Inc., Columbus, Ohio and D.E.R.® 331,D.E.R.® 332, D.E.R.® 334, and D.E.R.® 439, available from Dow ChemicalCo., Midland, Mich.

Other suitable bisphenol-A epoxy resins include Bisphenol A propoxylatediglycidyl ether, which is also commercially available, e.g., fromSigma-Aldrich, Inc. and which has the following structure:

wherein n=1.

Other suitable glycidyl ether epoxy resins comprising aromatic moietiesinclude bis(4-hydroxyphenyl)methane (known as bisphenol F) anddiglycidyl ether of bromobisphenol A(2,2-bis(4-(2,3-epoxypropoxy)3-bromo-phenyl)propane). Bisphenol-F basedepoxy resins are commercially available, for example D.E.R.® 354 andD.E.R.® 354LV, each available from The Dow Chemical Company, Midland,Mich.

Additional glycidyl ether epoxy resins comprising aromatic moieties thatmay be used with the instant compositions include phenol and cresolnovolacs. As is known in the art, these epoxies may be prepared byreacting phenols or cresols, in excess, with formaldehyde in thepresence of an acidic catalyst to produce phenolic novolac resin.Novolac epoxy resins are then synthesized by reacting the phenolicnovolac resin with epichlorohydrin in the presence of sodium hydroxideas a catalyst. A representative phenol novalac is depicted below,wherein “n” is a number of repeat units, which may, for example rangefrom 0 to 5.

wherein n=0-5

Examples of epoxy phenolic novolac resins including epoxy bisphenol Anovolac resins useful in some embodiments disclosed herein include thoseavailable under the tradenames D.E.R.® 431 and D.E.R.® 438 from The DowChemical Company, Midland, Mich., and EPON® SU-8, available from HexionSpecialty Chemicals, Columbus, Ohio.

Other suitable epoxy resins containing aromatic groups include thosethat can be prepared by the reaction of aromatic alcohols such asbiphenyl diols and triphenyl diols and triols with epichlorohydrin. Onerepresentative compound is tris-(hydroxyl phenyl)methane-based epoxyavailable from Huntsman Corporation, Basel, Switzerland as Tactix® 742.

Additional suitable epoxy resins include glycidal amines. Glycidalamines are formed by reacting epichlorohydrin with an amine, such as anaromatic amine. An example of a suitable glycidal amine is tetraglycidylmethylene dianiline, which is represented by the following structure:

Additional suitable epoxy resins include aliphatic epoxy resins.Aliphatic epoxy resins are known in the art and include glycidyl epoxyresins and cycloaliphatic epoxides. Glycidyl aliphatic epoxy resins maybe formed by the reaction of epichlorohydrin with aliphatic alcohols orpolyols to give glycidyl ethers or aliphatic carboxylic acids to giveglycidyl esters. This reaction may be done in the presence of an alkali,such as sodium hydroxide, to facilitate the dehydrochlorination of theintermediate chlorohydrin. These resins generally display low viscosityat room temperature, such as a viscosity ranging from about 10 to about200 mPa·s. Exemplary glycidyl aliphatic epoxy resins for use in theconductive adhesive composition disclosed herein includetrimethylolpropane triglycidyl ether, neopentyl glycol diglycidyl ether,and poly(propylene glycol) diglycidyl ether, which are commerciallyavailable, for example, from Sigma-Aldrich, Inc.

Cycloaliphatic epoxides may also be included in the presentcompositions. Cycloaliphatic epoxides contain one or more cycloaliphaticrings in the molecule to which an epoxide ring is fused. They are formedby the reaction of cyclo-olefins with a peracid, such as peracetic acid.Cycloaliphatic epoxides suitable for use in preparing the instantcompositions include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexylmethyl)adipate, vinyl cyclohexanedioxide, and the like and are commercially available from, for example,Union Carbide Corporation, a subsidiary of the Dow Chemical Company,Houston, T.X.

One or more epoxy resins can be provided in the conductive adhesivecompositions disclosed herein in any suitable or desired amount. Incertain embodiments, the at least one epoxy resin is present in thecomposition in an amount ranging from about 0.01 to about 40 percent,such as from about 5 to about 35 percent, or from about 10 to about 25percent, by weight, based on the total weight of the composition.

Polyvinyl Phenol

The conductive adhesive compositions disclosed herein may comprise atleast one polymer chosen from polyvinyl phenols and polyvinyl butyrals.Polyvinyl phenols can include, for example, the following:poly(4-vinylphenol), poly-p-vinylphenol, poly(vinylphenol)/poly(methylacrylate), poly(vinylphenol)poly(methyl methacrylate), andpoly(4-vinylphenol)poly(vinyl methyl ketone).

The polyvinyl phenol can be provided in the composition in any suitableor desired amount. The amount of the polyvinyl phenol present in theinstant conductive adhesive composition in accordance with the presentdisclosure may range from about 1 wt % to about 20 wt %, such as fromabout 1 wt % to about 10 wt %, and from about 1 wt % to about 5 wt %,based on the total weight of the conductive adhesive composition.

Polyvinyl Butyral

The conductive adhesive compositions disclosed herein may comprise atleast one of polyvinyl phenols and polyvinyl butyrals. As used herein,“polyvinyl butyral” refers to a product obtained from the hydrolysis ofpolyvinyl acetate to form polyvinyl alcohol or a polyvinyl alcoholpolymer containing residual vinyl acetate groups; the resultingpolyvinyl alcohol product being reacted with butyraldehyde under acidicconditions to form a polyvinyl butyral containing various amounts ofacetate, alcohol and butyraldehyde ketal groups. In some embodiments,the polyvinyl butyral is in the form of a powder or a pellet. Methods ofpreparing polyvinyl butyral are known in the art and are described forexample in U.S. Patent Publication No. 2012/0043512, which is hereinincorporated by reference in its entirety.

Polyvinyl butyral for use in the present composition may be representedby the following formula:

wherein A, B and C represent a proportion of the corresponding repeatunits expressed as a weight percent, wherein each repeat unit israndomly distributed along a polymer chain, and wherein the sum of A, Band C is about 100 weight percent.

In some embodiments, A is independently about 70 weight percent to about95 weight percent, about 75 weight percent to about 90 weight percent,or about 80 weight percent to about 88 weight percent; B isindependently about 5 weight percent to about 25 weight percent, about 7weight percent to about 20 weight percent or about 11 weight percent toabout 18 weight percent, such as about 17.5 weight percent; C isindependently about 0 weight percent to about 10 weight percent, about 0weight percent to about 5 weight percent or about 0 weight percent toabout 3 weight percent, such as about 2.5 weight percent.

In some embodiments, the polyvinyl butyral of Formula VI has an averagemolecular weight (M_(n)) of about 10,000 to about 300,000 Daltons (Da),about 40,000 to about 200,000 Da or about 25,000 to about 150,000 Da. Arepresentative composition of the polyvinyl butyral constitutes, on aweight basis, about 11% to 25% hydroxyl groups, calculated as polyvinylalcohol, about 0% to about 2.5% acetate groups calculated aspolyvinylacetate, with the balance being vinyl butyral groups, forexample, about 80 wt % to about 88 wt %.

Suitable polyvinyl butyral for use with the conductive adhesivecompositions disclosed herein are commercially available and include,for example, Butvar® B-79 (available from Monsanto Chemical Co., St.Louis, Mo.) having a polyvinyl butyral content of about 88 wt %, apolyvinyl alcohol content of about 11.0 wt % to about 13.5 wt %, and apolyvinyl acetate content of less than about 2.5 wt %, wherein theaverage molecular weight of Butvar® B-79 is from about 50,000 to about80,000 Da. In certain embodiments, Butvar® B-76 (Monsanto Chemical Co.)may be used in the conductive adhesive composition. Butvar® B-76 has apolyvinyl butyral content of about 88% by weight, a polyvinyl alcoholcontent of about 11.5 wt % to about 13.5 wt %, and a polyvinyl acetatecontent of less than about 2.5 wt %, with an average molecular weight ofabout 90,000 to about 120,000 Da. Suitable polyvinyl butyrals for usewith the conductive adhesive compositions may also include, for example,Butvar® B-72, Butvar® B-74, Butvar® B-90, and Butvar® B-98 (availablefrom Monsanto Chemical Co., St. Louis, Mo.).

The polyvinyl butyral can be provided in the composition in any suitableor desired amount. The amount of the polyvinyl butyral present in theinstant conductive adhesive composition in accordance with the presentdisclosure may range from about 1 wt % to about 20 wt %, such as fromabout 1 wt % to about 10 wt %, and from about 1 wt % to about 5 wt %,based on the total weight of the conductive adhesive composition.

Melamine Resin

In some embodiments, the conductive adhesive composition furtherincludes a cross-linking agent, such as a melamine resin, such as amelamine-formaldehyde based polymer. As used herein, the term“melamine-formaldehyde based polymer” refers to polymers formed by acondensation reaction of melamine (1,3,5-triazine-2,4,6-triamine) withformaldehyde (CH₂O). In some embodiments, the free hydroxyl groups ofthe polyvinyl phenol and/or polyvinyl butyral may bond with themelamine-formaldehyde based polymer. Thus, the polyvinyl phenol and/orpolyvinyl butyral may be substituted with or “cross-linked” by themelamine-formaldehyde based polymer.

Any suitable or desired melamine-formaldehyde based polymer may beincluded in the conductive adhesive compositions disclosed herein. Insome embodiments, the poly(melamine-co-formaldehyde) based polymer isrepresented by the following chemical structure:

where R is independently selected from hydrogen (H) and an alkyl, suchas methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, and isomersthereof, and in is a number of repeats of thepoly(melamine-co-formaldehyde). For example, m may be a number betweenabout 1 and about 10. As a non-limiting example, the number molecularweight (Mn) range for the poly(melamine-co-formaldehyde) based polymermay be from about 300 grams/mole to about 1,500 grams/mole. Suitablepoly(melamine-co-formaldehyde) based polymers may be obtainedcommercially from Sigma-Aldrich, Inc. (Saint Louis, Mo.), a subsidiaryof Merck KGaA.

In another embodiment, the melamine-formaldehyde based polymer is anacrylated melamine-formaldehyde based polymer, represented by thefollowing Formula X, wherein “m” is the number of repeats of thepoly(melamine-co-formaldehyde), such as between 1 and 10, and R is H,CH₃ or C₄H₉.

In certain embodiments, m ranges from about 1 to about 10, such as about2 to about 8 or about 3 to about 7.

Acrylated melamine-formaldehyde based polymers are commerciallyavailable from Sigma-Aldrich, Inc., for example, and may have amolecular weight ranging from about 390 grams/mole to about 1,500grams/mole.

In some embodiments, the poly(melamine-co-formaldehyde) based polymer isselected from the group consisting of methylatedpoly(melamine-co-formaldehyde), butylatedpoly(melamine-co-formaldehyde), isobutylatedpoly(melamine-co-formaldehyde), acrylatedpoly(melamine-co-formaldehyde), methylated/butylatedpoly(melamine-co-formaldehyde), and combinations thereof.

The poly(melamine-co-formaldehyde) based polymer can be provided in theconductive adhesive composition in any suitable or desired amount. Insome embodiments, the poly(melamine-co-formaldehyde) polymer is presentin an amount ranging from about 0.5 percent to about 15 percent, such asfrom about 1 percent to about 10 percent, or from about 1 percent toabout 5 percent, by weight, based on the total weight of the conductiveadhesive composition.

Eutectic Metal Alloy Nanoparticles

The conductive adhesive compositions disclosed herein comprise aplurality of eutectic metal alloy nanoparticles. Suitable eutectic metalalloys for use in the present composition include those eutectic metalalloys having a melting point lower than that of the melting point ofthe substrate upon which a conductive ink composition may be depositedand sintered. For example, in certain embodiments, the melting points ofsuitable eutectic metal alloys may be about 140° C. or less, such asabout 55° C. to about 75° C., about 60° C. to about 65° C., or about60.5° C. Eutectic metal alloys may be comprised of, for example, atleast two metals chosen from bismuth, lead, tin, cadium, zinc, indium,gallium, and thallium. For example, the eutectic metal alloys mayinclude at least two of bismuth, tin, indium, and gallium, or, incertain embodiments, the eutectic metal alloy disclosed herein mayinclude indium, bismuth, and tin. In certain embodiments, the eutecticmetal alloy is chosen from In_(51.0)Bi_(32.5)Sn_(16.5), i.e., Field'sMetal (which may, for example, have a melting point of about 60.5° C.),Bi₅₈Sn₄₂ (which may, for example, have a melting point of about 138°C.), In_(66.3)Bi_(33.7) (which may, for example, have a melting point ofabout 72° C.), and Bi₅₇Sn₄₃ (which may, for example, have a meltingpoint of about 139° C.). As used herein, “Field's metal” refers to aeutectic, low-melting alloy of bismuth, indium, and tin. In certainexemplary embodiments, the Field's metal is In_(51.0)Bi_(32.5)Sn_(16.5).In other embodiments disclosed herein, the eutectic metal alloy mayfurther include at least one organic vehicle, such as an organic solventand/or a stabilizer as described herein.

The average particle size of the eutectic metal alloy nanoparticles maybe about 1000 nanometers (nm) or less. In certain embodiments, theaverage particle size of the eutectic metal alloy nanoparticles mayrange from about 0.5 nm to about 1000 nm or from about 0.5 nm to lessthan about 1000 nm, such as from about 1 nm to about 750 nm, from about10 nm to about 500 nm, from about 50 nm to about 400, from about 75 nmto about 250 nm, from about 100 nm to about 200 nm, or from about 100 nmto about 150 nm. In certain embodiments, the median diameter (D50) ofthe eutectic metal alloy nanoparticles may range from about 0.5 nm toabout 1000 nm or from about 0.5 nm to less than about 1000 nm, such asfrom about 1 nm to about 750 nm, from about 10 nm to about 500 nm, fromabout 50 nm to about 400, from about 75 nm to about 250 nm, from about100 nm to about 225 nm, or from about 150 nm to about 200 nm. Theaverage particle size and median diameter of the particles may bedetermined by any suitable means, such as, for example, lightmicroscopy, Scanning Electron Microscopy (SEM), or, for example, byusing a Nanotrac® particle size analyzer.

The eutectic metal alloy nanoparticles disclosed herein may, in certainembodiments, have properties distinguishable from those of otherconductive components often used in conductive composition, such assilver flakes. For example, the eutectic metal alloy nanoparticlesdisclosed herein may be characterized by a high surface tension.Further, the present eutectic metal alloy nanoparticles may have a lowermelting point and a lower sintering temperature than silver flakes. Thehigh surface tension prevents the eutectic metal alloy nanoparticlesfrom flowing at temperatures above the melting temperature of theeutectic metal alloy. In order for the eutectic metal composition toflow, an external stimulus, such as pressure, may be placed on thecomposition. In embodiments, the conductive adhesive compositioncomprising eutectic metal alloy nanoparticles may be heated above themelting temperature of the eutectic metal alloy (i.e., ≥62° C.) andpressure may be applied to the composition in the form of placing aresistor chip onto the composition.

In embodiments disclosed herein, the surface tension of the conductiveadhesive composition comprising eutectic metal alloy nanoparticles mayrange from about 20 nM/m to about 60 nM/m, such as about 25 nM/m toabout 45 nM/m or about 30 nM/m to about 35 nM/m. Surface tension bemeasured in units of force per unit length (newtons per meter), energyper unit area (joules/square meter), or the contact angle between thesolvent and a glass surface. Surface tension may be measured by anymeans known in the art, for example with a Kruss K-100 Tensiometer.

The eutectic metal alloy nanoparticle component of the conductiveadhesive compositions disclosed herein may be present in any suitable ordesired amount. In certain embodiments, the eutectic metal alloynanoparticles, such as the Field's metal nanoparticles, are present inthe conductive adhesive composition in an amount ranging from about 60%to about 95%, such as about 70% to about 90%, about 75% to about 85%, orabout 80%, by weight based on the total solids weight of the conductiveadhesive composition.

The eutectic metal alloy nanoparticles disclosed herein may be preparedby any suitable method. One exemplary method is to add pieces, such ascentimeter sized chunks, of the eutectic metal alloy disclosed herein toa heated mixture comprising at least one solvent and at least oneorganic stabilizer, such as an organoamine stabilizer, until the alloyis molten and a mixture is formed. The mixture may then be dispersed bysonication and cooled. The eutectic metal alloy nanoparticles may thenbe isolated by decantation, rinsed, and dried.

Prior to, during, or after mixing the at least one organic stabilizer tothe at least one solvent, the solvent may be heated, for example, to atemperature above the melting point of the eutectic metal alloynanoparticles. In certain embodiments, the solvent may be heated to atemperature greater than about 55° C., such as about 60° C., about 65°C., about 70° C., or about 75° C.

The sonication can be performed by probe sonication or by bathsonication. Probe sonication refers to sonication wherein a probe isinserted into a container containing the mixture. Bath sonication refersto sonication wherein the container containing the mixture is placedinto a bath, and the bath is subsequently sonicated. Probe sonicationmay provide greater energy and/or power compared to bath sonication.

In certain embodiments, the mixture may be sonicated at any suitablepower, such as a power ranging from about 20% to about 100%, such asabout 50% to about 90%, about 60% to about 80%, or, in certainembodiments, at about 100% power. The mixture may be sonicated for anysuitable amount of time, such as, for example, from about 1 minute toabout 1 hour, or, in certain embodiments, from about 2 minutes to about45 minutes, about 5 minutes to about 20 minutes, or about 8 minutes toabout 15 minutes. Any desired or effective sonicator can be used, suchas a Branson Digital Probe Sonifier®. During sonication, the dispersionmay be iced in order to cool the dispersion. In certain embodiments, thedispersion may be placed in an ice bath while sonicating in order tomaintain the temperature of the dispersion below a certain temperature,such as, for example, below about 100° C., below about 85° C., or belowabout 75° C. After sonication, the dispersion may be cooled, for examplecooled to about room temperature. The dispersed nanoparticles may thenbe collected, for example by centrifugation and decantation of thesolvent, which may be repeated as necessary. Finally, the nanoparticlesmay be dried.

The at least one organic stabilizer that may be used in the preparationof the eutectic metal alloy nanoparticles disclosed herein may bephysically or chemically associated with the surface of the eutecticmetal alloy nanoparticles. In this way, the nanoparticles have thestabilizer thereon outside of a liquid solution. That is, thenanoparticles with the stabilizer thereon may be isolated and recoveredfrom a reaction mixture solution used in forming the nanoparticles andstabilizer complex. The stabilized nanoparticles may thus besubsequently ready and homogenously dispersed in a solvent for forming aconductive adhesive composition as disclosed herein.

The organic stabilizer may interact with the eutectic metal alloynanoparticle by a chemical bond and/or a physical attachment. Thechemical bond may take the form of, for example, covalent bonding,hydrogen bonding, coordination complex bonding, ionic bonding, or amixture of different chemical bonds. The physical attachment may takethe form of, for example, van der Waals' forces, dipole-dipoleinteractions, or a mixture of different physical attachments.

The term “organic” in “organic stabilizer” refers to, for example, thepresence of carbon, but, in addition to carbon, the organic stabilizermay include one or more non-metal heteroatoms such as nitrogen, oxygen,sulfur, silicon, halogen, and the like.

Exemplary organic stabilizers can include organoamines such aspropylamine, butylamine, pentylamine, hexylamine, heptylamine,octylamine, nonylamine, decylamine, undecylamine, tridecylamine,tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine,octadecylamine, N,N-dimethylamine, N,N-dipropylamine, N,N-dibutylamine,N,N-dipentylamine, N,N-dihexylamine, N,N-diheptylamine,N,N-dioctylamine, N,N-dinonylamine, N,N-didecylamine,N,N-diundecylamine, N,N-didodecylamine, dodecylamine, methylpropylamine,ethylpropylamine, propylbutylamine, ethylbutylamine, ethylpentylamine,propylpentylamine, butylpentylamine, triethylamine,triethylenepentamine, tripropylamine, tributylamine, tripentylamine,trihexylamine, triheptylamine, trioctylamine, 1,2-ethylenediamine,N,N,N′,N′-tetramethylethylenediamine, propane-1,3-diamine,N,N,N′,N′-tetramethylpropane-1,3-diamine, butane-1,4-diamine,N,N,N′,N′-tetramethylbutane-1,4-diamine, diaminopentane, diaminoheptane,diaminooctane, diaminononane, diaminodecane,2,2-(ethylenedioxy)diethylamine, 3-methoxypropylamine,pentaethylenehexamine, diethylenetriamine, tetraethylenepentamine, andthe like or mixtures thereof. Exemplary organoamine stabilizers includebutylamine, octylamine, dodecylamine 2,2-(ethylenedioxy)diethylamine,3-methoxypropylamine, pentaethylenehexamine, tetraethylenepentamine,triethylenetetramine, and diethylenetriamine.

The extent of the coverage of the at least one organic stabilizer on thesurface of the eutectic metal alloy nanoparticles may vary, for example,from partial to full coverage depending on the capability of the organicstabilizer to stabilize the nanoparticles.

The at least one solvent used in the preparation of the eutectic metalalloy nanoparticles may include, for example, propylene glycol methylether acetate, propylene glycol monomethyl ether acetate, toluene,di(propylene glycol) methyl ether acetate, (propylene glycol) methylether, di(propylene glycol) methyl ether, methyl isobutyl ketone,diisobutyl ketone, butyl acetate, methoxypropylacetate, propoxylatedneopentylglycoldiacrylate, 1-phenoxy-2-propanol, and combinationsthereof. In certain embodiments, the at least one polar solvent ispropylene glycol methyl ether acetate. In embodiments, the solvent isnot water, and in certain embodiments, the composition comprising aplurality of eutectic metal alloy nanoparticles is free of water. Asused herein, “free of water,” indicates that the composition does notcontain a detectable quantity of water or that the composition isanhydrous.

Surfactants

Any suitable or desired surfactant can optionally be included in theconductive adhesive compositions disclosed herein. In certainembodiments, the at least one surfactant is selected from the groupconsisting of silicone modified polyacrylates, polyester modifiedpolydimethylsiloxanes, polyether modified polydimethylsiloxanes,polyacrylate modified polydimethylsiloxanes, polyester polyethermodified polydimethylsiloxanes, low molecular weight ethoxylatedpolydimethylsiloxanes, polyether modified polydimethylsiloxanes,polyester modified polymethylalkylsiloxanes, polyether modifiedpolymethylalkylsiloxanes, aralkyl modified polymethylalkylsiloxanes,polyether modified polymethylalkylsiloxanes, polyether modifiedpolydimethylsiloxanes, and combinations thereof.

For example, the surfactant may be a polysiloxane copolymer thatincludes a polyester modified polydimethylsiloxane, commerciallyavailable from BYK-Chemie GmbH, Wesel, Germany with the trade name ofBYK® 310; a polyether modified polydimethylsiloxane, commerciallyavailable from BYK-Chemie GmbH with the trade name of BYK® 330; apolyacrylate modified polydimethylsiloxane, commercially available fromBYK Chemical with the trade name of BYK® Silclean® 3700 (about 25 weightpercent in methoxypropylacetate); or a polyester polyether modifiedpolydimethylsiloxane, commercially available from BYK-Chemie GmbH withthe trade name of BYK® 375. The surfactant can also be a low molecularweight ethoxylated polydimethylsiloxane with the trade name Silsurf®A008 available from Siltech Corporation, Ontario, Canada. Some otherexamples of suitable surfactants may include BYK® 3500, BYK® 3510, BYK®307, BYK® 333, BYK® Anti-Terra® U100, BYK® A-004, and BYK® C-409.

One or more surfactants can be provided in the conductive adhesivecomposition disclosed herein in any suitable or desired amount. In someembodiments, the surfactant is present in an amount ranging from about0.01 to about 5 percent, such as from about 0.1 to about 3.5 percent, orfrom about 0.5 to about 2 percent, by weight, based on the total weightof the conductive adhesive composition.

Catalysts

The conductive adhesive compositions disclosed herein can optionallycomprise at least one catalyst to enhance the curing process. Anysuitable or desired catalyst can be selected for use in the presentcompositions. In certain embodiments, the at least one catalyst may beselected from the group consisting of amine salts of dodecylbenzenesulfonic acid (DDB SA), para toluene sulfonic acid, triflouromethanesulfonic acid, and combinations thereof.

The at least one catalyst can be provided in the conductive adhesivecomposition in any suitable or desired amount. In certain embodiments,the at least one catalyst is present in an amount ranging from about0.05 to about 1.5 percent, such as from about 0.08 to about 1.0 percent,or from about 0.1 to about 0.5 percent, by weight, based on the totalweight of the conductive adhesive composition.

Adhesion Promoters

In certain embodiments, the conductive adhesive composition disclosedherein may comprise at least one adhesion promoter, in any suitable ordesired amount. Exemplary adhesion promoter that may be envisionedinclude Sartomer® CN132 (aliphatic diacrylate oligomer), and Sartomer®CN133 (aliphatic triacyl oligomer).

Solvents

Any suitable or desired solvent can be selected for the presentconductive adhesive compositions. In some embodiments, the at least onesolvent is selected from the group consisting of propylene glycol methylether acetate (PGMEA), di(propylene glycol) methyl ether acetate(Di-PGMEA), (propylene glycol)methyl ether (PGME), di(propyleneglycol)methyl ether (Di-PGME), methyl isobutyl ketone (MIBK), diisobutylketone (DIBK), toluene, methyl isobutyl ketone, butylacetate,methoxypropylacetate, xylene, tripropyleneglycol monomethylether,dipropyleneglycol monomethylether, propoxylatedneopentylglycoldiacrylate, and combinations thereof.

In certain embodiments, the solvent can be a non-polar organic solventselected from the group consisting of hydrocarbons such as alkanes,alkenes, alcohols having from about 7 to about 18 carbon atoms such asundecane, dodecane, tridecane, tetradecane, hexadecane, 1-undecanol,2-undecanol, 3-undecanol, 4-undecanol, 5-undecanol, 6-undecanol,1-dodecanol, 2-dodecanol, 3-dedecanol, 4-dedecanol, 5-dodecanol,6-dodecanol, 1-tridecanol, 2-tridecanol, 3-tridecanol, 4-tridecanol,5-tridecanol, 6-tridecanol, 7-tridecanol, 1-tetradecanol,2-tetradecanol, 3-tetradecanol, 4-tetradecanol, 5-tetradecanol,6-tetradecanol, 7-tetradecanol, and the like; alcohols such as terpineol(α-terpineol), β-terpineol, geraniol, cineol, cedral, linalool,4-terpineol, 3,7-dimethylocta-2,6-dien-1ol,2-(2-propyl)-5-methyl-cyclohexane-1-ol; isoparaffinic hydrocarbons suchas isodecane, isododecane; commercially available mixtures ofisoparaffins such as Isopar® E, Isopar® G, Isopar® H, Isopar® L, Isopar®V, Isopar® G, manufactured by Exxon Chemical Company; Shellsol®manufactured by Shell Chemical Company; Soltrol® manufactured by ChevronPhillips Chemical Company; Begasol® manufactured by Mobil Petroleum Co.,Inc.; IP Solvent 2835 manufactured by Idemitsu Petrochemical Co., Ltd;naphthenic oils; aromatic solvents such as benzene, nitrobenzene,toluene, ortho-, meta-, and para-xylene, and mixtures thereof;1,3,5-trimethylbenzene (mesitylene); 1,2-, 1,3-, and 1,4-dichlorobenzeneand mixtures thereof, trichlorobenzene; cyanobenzene; phenylcyclohexaneand tetralin; aliphatic solvents such as isooctane, nonane, decane,dodecane; cyclic aliphatic solvents such as dicyclohexyl and decalin;and mixtures and combinations thereof.

In certain embodiments, two or more solvents can be used.

One or more solvents can be included in the conductive adhesivecomposition in any suitable or desired amount. In some embodiments, thesolvent is present in an amount ranging from about 50 to about 90percent, such as from about 60 to about 80 percent or from about 70 toabout 80 percent, by weight, based on the total weight of the conductiveadhesive composition.

Percent Solids

In some embodiments, the conductive adhesive compositions disclosedherein comprise from about 10 to about 60 weight percent solids, such asfrom about 15 to about 45 weight percent solids, or from about 20 toabout 40 weight percent solids, based on the total weight of thecomposition in accordance with the present disclosure. In certainembodiments, the conductive adhesive composition contains a selectedsolids content of less than about 50 weight percent solids, based on thetotal weight of the instant composition. In certain embodiments, theeutectic metal alloy nanoparticles comprise about 60 weight percent toabout 95 weight percent, such as from about 75 weight percent to about90 weight percent, or about 80 weight percent to about 85 weight percentof the composition, based on the total solids weight of the composition.

Electronic Devices

In certain embodiments, disclosed herein is an electronic deviceincluding a substrate, a set of conductive terminals on the substrate,an electronic component opposite the substrate, a set of conductiveterminals attached to the electronic component and facing the substrate,and a conductive adhesive composition, such as an anisotropic conductiveadhesive composition, disposed between the electronic component and thesubstrate. The conductive adhesive composition may comprise conductiveparticles, such as eutectic metal alloy nanoparticles, distributed in aninsulating medium in a substantially uniform manner.

An exemplary application of an anisotropic conductive adhesivecomposition includes a group of conductive elements. The composition ispositioned between two sets of conductive terminals. A charge or fieldis generated by or passed through a substrate, which may be flexible, tothe terminals. The field may pass from one terminal to another terminalthrough the anisotropic conductive adhesive composition. A top layer,such as an electronic component like a resistor, may comprise a set ofconductive contact pads and may cover the anisotropic conductiveadhesive composition and the terminals.

To create conductivity from the terminals to the electronic componentthrough the conductive particles, the anisotropic conductive adhesivecomposition may be sandwiched between the top and bottom layers, i.e.,between the substrate and the electronic component. When sandwiched inbetween, the conductive particles, such as eutectic metal alloynanoparticles, may deform and provide a larger conductive surface areathat contacts the terminals and conductive contact pad.

The substrate may be any suitable substrate including silicon, a glassplate, a plastic film, sheet, fabric, synthetic paper, or mixturesthereof. For structurally flexible devices, plastic substrates such aspolyester, polycarbonate, polyimide sheets, polyethylene terephthalate(PET) sheets, polyethylene naphthalate (PEN) sheets, and the like,including mixtures thereof, may be used. The thickness of the substratecan be any suitable thickness, such as from about 10 micrometers to over10 millimeters with an exemplary thickness being from about 50micrometers to about 2 millimeters, especially for a flexible plasticsubstrate, and from about 0.4 to about 10 millimeters for a rigidsubstrate such as glass or silicon.

As shown in FIGS. 1 and 2, in certain exemplary embodiments of theelectrical devices disclosed herein, there is a substrate 10, at leasttwo areas formed from conductive ink 11 on the surface of the substrate10, a conventional electronic component 15, such as a resistor,comprising at least two conductive contact pads 14 positioned over theat least two areas formed from conductive ink, and an adhesiveconductive composition 12 disposed in between the conductive ink 11 andthe conventional electronic component 15, wherein the adhesiveconductive composition 12 comprises eutectic metal alloy nanoparticles13.

In certain embodiments, the areas formed from conductive ink 11 may bespaced such that there is a gap 17 between a first area 11 and a secondarea 11 formed from conductive ink. In various embodiments of thedisclosure, the adhesive conductive composition 12 comprising eutecticmetal alloy nanoparticles 13 is not disposed inside the gap 17, suchthat the adhesive conductive composition 12 is on the surface of theareas formed from conductive ink 11. See, e.g., FIGS. 1A-C. In certainembodiments, the adhesive conductive composition 12 comprising eutecticmetal alloy nanoparticles 13 is disposed inside the gap 17, such thatthe adhesive conductive composition 12 is both on the surface of theareas formed from conductive ink 11 and on the surface of the substrate10. See, e.g., FIGS. 2A and 2B.

The conductive adhesive composition may be disposed on the substrateand/or conductive ink using any suitable method. For example, thepresent composition may be disposed on the substrate and/or conductiveink by solution depositing. Solution depositing as used herein refers toa process whereby a liquid is deposited upon the substrate to form acoating or layer. Solution depositing includes, for example, one or moreof spin coating, dip coating, spray coating, slot die coating,flexographic printing, offset printing, screen printing, gravureprinting or ink jet printing the conductive adhesive composition ontothe substrate and/or conductive ink. In certain embodiments, theconductive adhesive composition is disposed on the substrate and/orconductive ink by ink jet printing.

In some embodiments, the conductive adhesive composition disposed on thesubstrate and/or the conductive ink is cured. The conductive adhesivecomposition can be cured at any suitable or desired temperature for anysuitable period of time. In some embodiments, the conductive adhesivecomposition can be cured at a temperature ranging from about 80° C. toabout 200° C., such as from about 100° C. to about 180° C., or fromabout 120° C. to about 160° C. for a period of time ranging from about0.5 to about 6 hours, from about 1 to about 4 hours, or from about 2 toabout 3 hours. In embodiments, the present composition can be cured atabout 160° C. for about 6 hours or at about 200° C. for about 0.5 hours.

In some embodiments, the electronic device includes a conductivematerial. Any suitable or desired conductive material can be used toform conductive features on the present device. Typically, a conductivecomposition, such as a metal ink composition, is used to provide theconductive features, and suitable metal ink compositions may include,for example, silver nanoparticles dispersed within an ink vehicle, suchas aromatic hydrocarbons including benzene, toluene, xylene andethylbenzene. The fabrication of conductive features, such as anelectrically conductive element, from a metal ink composition, forexample, from a nanoparticle metal ink, such as a nanosilver inkcomposition, can be carried out by depositing the nanosilver inkcomposition, for example, onto a substrate using any suitable depositiontechnique including solution processing as described herein.

In some embodiments, the conductive features are formed by heating theconductive composition. In some embodiments, prior to heating, the layerof the deposited conductive composition may be electrically insulatingor may have very low electrical conductivity; however, heating resultsin an electrically conductive layer composed of annealed metalparticles, for example, such as annealed eutectic metal alloynanoparticles, which increases the conductivity.

The deposited conductive composition, such as a metal ink composition,is heated to any suitable or desired temperature, such as from about 70°C. to about 250° C., or any temperature sufficient to induce annealingof the metal particles, for example, and thus form an electricallyconductive layer, which is suitable for use as an electricallyconductive element in electronic devices. The heating temperature is onethat does not cause adverse changes in the properties of previouslydeposited layers or the substrate. In some embodiments, use of lowheating temperatures allows use of low cost plastic substrates, whichhave an annealing temperature of below 140° C.

The heating can be for any suitable or desired time, such as from about0.01 hours to about 10 hours. The heating can be performed in air, in aninert atmosphere, for example under nitrogen or argon, or in a reducingatmosphere, for example, under nitrogen containing from about 1 to about20 percent by volume hydrogen. The heating can also be performed undernormal atmospheric pressure or at a reduced pressure of, for example,about 1000 mbars to about 0.01 mbars.

Heating encompasses any technique that can impart sufficient energy tothe heated material or substrate to anneal the metal nanoparticles, forexample. These techniques include thermal heating (for example, at hotplate, an oven, and a burner), infra-red (“IR”) radiation, laser beam,flash light, microwave radiation, or ultraviolet (“UV”) radiation, or acombination thereof.

In some embodiments, after heating, an electrically conductive line,such as an electrically conductive silver line, is formed on thesubstrate that has a thickness ranging from about 0.1 to about 20micrometers, or from about 0.15 to about 10 micrometers. In certainembodiments, after heating, the resulting electrically conductive linehas a thickness of from about 0.1 to about 2 micrometers.

The conductivity of the conductive features, such as an electricallyconductive line, that is produced by heating the deposited conductivecomposition is more than about 10,000 Siemens/centimeter (S/cm), morethan about 50,000 S/cm, more than about 80,000 S/cm, more than about100,000 S/cm, more than about 125,000 S/cm, more than about 150,000 S/cmor more than about 200,000 S/cm. Typically, the conductivity ranges fromabout 50,000 S/cm to about 200,000 S/cm, such as about 80,000 S/cm toabout 150,000 S/cm, such as about 100,000 S/cm to about 125,000 S/cm.

The resistivity of the conductive features, such as an electricallyconductive line, that is produced by heating the deposited conductivecomposition is less than about 1.0×10⁻⁴ ohms-centimeter (ohms-cm), lessthan about 2.0×10⁻⁵ ohms-cm, less than about 1.25×10⁻⁵ ohms-cm, lessthan about 1.0×10⁻⁵ ohms-cm, less than about 8.0×10⁻⁶ ohms-cm, less thanabout 6.6×10⁻⁶ ohms-cm or less than about 5.0×10⁻⁶ ohms-cm. Typically,the resistance ranges from about 2.0×10⁻⁵ ohms-cm to about 5.0×10⁻⁶ohms-cm, such as about 1.25×10⁻⁵ ohms-cm to about 6.6×10⁻⁶ ohms-cm, suchas about 1.0×10⁻⁵ ohms-cm to about 8.0×10⁻⁶ ohms-cm.

The device of the present disclosure may be used for any suitable ordesired application, such as for electrodes, conductive pads,interconnects, conductive lines, conductive tracks, and the like, inelectronic devices such as thin film transistors, organic light emittingdiodes, printed antenna, and other electronic devices requiringconductive elements or components.

Cured Conductive Adhesive Compositions

Also provided herein is a cured conductive adhesive composition formedfrom a composition comprising at least one epoxy resin, at least onepolymer chosen from polyvinyl phenols and polyvinyl butyrals, at leastone melamine resin, eutectic metal alloy nanoparticles, and at least onesolvent as described herein.

In some embodiments, the cured conductive adhesive comprises conductivefeatures, such as an electrically conductive line, as described herein.In certain embodiments, the conductivity of the conductive features ofthe cured film is more than about 10,000 Siemens/centimeter (S/cm), morethan about 50,000 S/cm, more than about 80,000 S/cm, more than about100,000 S/cm, more than about 125,000 S/cm, more than about 150,000 S/cmor more than about 200,000 S/cm. For example, in certain embodiments,the conductivity of the cured conductive adhesive comprising theconductive features, such as an electrically conductive line, rangesfrom about 50,000 S/cm to about 200,000 S/cm, such as about 80,000 S/cmto about 150,000 S/cm, or about 100,000 S/cm to about 125,000 S/cm.

In some embodiments, the resistivity of the conductive features, such asan electrically conductive line of the cured conductive adhesive is lessthan about 1.0×10⁻⁴ ohms-centimeter (ohms-cm), less than about 2.0×10⁻⁵ohms-cm, less than about 1.25×10⁻⁵ ohms-cm, less than about 1.0×10⁻⁵ohms-cm, less than about 8.0×10⁻⁶ ohms-cm, less than about 6.6×10⁻⁶ohms-cm, or less than about 5.0×10⁻⁶ ohms-cm. In certain embodiments,the resistivity of the cured conductive adhesive comprising theconductive features, such as an electrically conductive line, rangesfrom about 2.0×10⁻⁵ ohms-cm to about 5.0×10⁻⁶ ohms-cm, such as about1.25×10⁻⁵ ohms-cm to about 6.6×10⁻⁶ ohms-cm, or about 1.0×10⁻⁵ ohms-cmto about 8.0×10⁻⁶ ohms-cm.

Methods of Forming Conductive Elements

The conductive adhesive compositions disclosed herein may be prepared bymixing the eutectic metal alloy nanoparticle component with a firstcomponent comprising the at least one epoxy resin, at least one polymerchosen from polyvinyl phenols and polyvinyl butyrals, the at least onemelamine resin, and the at least one solvent, as disclosed herein.

Also provided herein is a process for forming conductive features, suchas an electrically conductive line as described herein, on a substrateincluding depositing a conductive adhesive composition onto a substrateand/or conductive element, such as a conductive ink, as describedherein, and curing the conductive adhesive composition to form a curedconductive adhesive. The conductive features can be fabricated by anysuitable or desired method. In certain embodiments, the conductivefeatures can be prepared by solution processing techniques such as inkjet printing on the substrates with a pre-applied interlayer. Theconductive features show high conductivity with significantly improvedadhesion after annealing at a suitable temperature.

In certain embodiments, the conductive adhesive composition is depositedonto a substrate and/or conductive element by ink jet printing. Forexample, in certain embodiments, aerosol jet printing is used fordeposition. As used herein, “aerosol jet printing” refers to a processthat involves atomization of the conductive adhesive composition,producing droplets on the order of one to two microns in diameter. Theatomized droplets may be entrained in a gas stream and delivered to aprint head. At the print head, an annular flow of gas may be introducedaround the aerosol stream to focus the droplets into a tightlycollimated beam. The combined gas streams may then exit the print headthrough a converging nozzle that compresses the aerosol stream to asmall diameter, for example a diameter ranging from about 1 micron toabout 10 microns. The jet exits the print head and is deposited on asubstrate or other surface. The resulting patterns can have featuresranging from about 5 microns to about 3000 microns wide, with layerthickness ranging from tens of nanometers to about 25 microns, such asfrom about 1 micron to about 20 microns.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein.

While the present teachings have been illustrated with respect to one ormore implementations, alterations and/or modifications can be made tothe illustrated examples without departing from the spirit and scope ofthe appended claims. In addition, while a particular feature of thepresent teachings may have been disclosed with respect to only one ofseveral implementations, such feature may be combined with one or moreother features of the other implementations as may be desired andadvantageous for any given or particular function. Furthermore, to theextent that the terms “including,” “includes,” “having,” “has,” “with,”or variants thereof are used in either the detailed description and theclaims, such terms are intended to be inclusive in a manner similar tothe term “comprising.” Further, in the discussion and claims herein, theterm “about” indicates that the value listed may be somewhat altered, aslong as the alteration does not result in nonconformance of the processor structure to the illustrated embodiment. Finally, “exemplary”indicates the description is used as an example, rather than implyingthat it is an ideal.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompasses by the following claims.

EXAMPLES

The following Examples are being submitted to further define variousspecies of the present disclosure. These Examples are intended to beillustrative only and are not intended to limit the scope of the presentdisclosure. Parts and percentages are by weight unless otherwiseindicated.

Example 1A—Preparation of Base Adhesive Composition

Base adhesive solutions were prepared containing the formulation as setforth in Table 1 below.

TABLE 1 Formulation of Base Solution PLGDE Di-PGMEA (Mn 380) PMMF PVPPGMEA solvent Di-PGME Solid Total (g) (g) (g) (g) (g) (g) (%) (wt %)13.2 2.8 2.5 16.5 15.0 37.0 50.0 35.7 7.6 6.7 50.0 50.0 100.0 13.2 3.753.75 29.30 50.0 PLGDE—polypropylene glycol diglycidyl etherPMMF—poly(melamine-co-formaldehyde) PVP—polyvinyl phenol PGMEA—propyleneglycol methyl ether acetate Di-PGMEA—di(propylene glycol) methyl etheracetate Di-PGME—di(propylene glycol)methyl ether

A 60 mL bottle (Bottle A) and a 125 mL bottle (Bottle B) were air-blownto clean, and a magnetic stir bar was added into each bottle. Bottle Band its lid were weighed, and the weight recorded. 16.5 g ofdi(propylene glycol) methyl ether acetate (Di-PGMEA) solvent was loadedinto Bottle A, and then 2.8 g poly(melamine-co-formaldehyde) (PMMF) wasadded. Bottle A was stirred at 250 rpm and run for at least 5 minutesuntil the PMMF was completely dissolved. Next, 15 g of di(propyleneglycol)methyl ether (Di-PGME) solvent was added to Bottle B, followed by13.2 g polypropylene glycol diglycidyl ether (PLGDE), and the solutionwas mixed for at least 5 minutes.

The contents of Bottle A and Bottle B were combined by pouring thesolution of Bottle A into Bottle B, and the combined solutions weremixed for about 30 minutes. Next, 2.5 g of polyvinyl phenol (PVP) wasslowly added into Bottle B and then mixed for two hours, until all ofthe PVP powder was dissolved.

Example 1B—Preparation of Conductive Adhesive Composition

To a 30 mL bottle was loaded 7.5 g of a base adhesive composition,having a solids content of 2.775 g (7.5 g×37%) and 7.5 g of di(ethyleneglycol) methyl ether (Di-PGME) and di(ethylene glycol methyl etheracetate (Di-PGMEA) mixture at a ratio of 1:1. The bottle was then put ona Vortex for 5 seconds at a setting speed of 3000 rpm. Next, the bottlewas rolled on a Roller for about 5 minutes. 10 g of Field's Metalparticles were added, such that the amount of Field's Metal after dryingwas about 78.3% (10/(10+7.5*0.37)*100). The bottle was put on a Vortexfor 10 seconds at a setting speed of 3000 rpm, and then stirred with amagnetic rod overnight. The resultant sample was placed into a waterbath sonicator for 10 minutes before aerosol print testing.

Example 1C—Characterization of Conductive Adhesive Composition

The conductive adhesive composition prepared in Example 1B was evaluatedto analyze the Field's Metal particle size distribution, as well asother physical characteristics of the composition. Field's Metalnanoparticles were synthesized using tetraethylenepentamine as theorganoamine stabilizer. Particle size was analyzed using a Nanotrac®U2275E, and the results are shown below in Tables 2A and 2B. The mediandiameter (D50) was 193 nm (0.193 μm), and 98.1% of the particles were<192 nm (0.1918 μm) with an average particle size of 148.6 nm (0.1486μm).

TABLE 2A Particle Size Distribution for Eutectic Metal AlloyNanoparticles with Tetraethylenepentamine Percentile Size (nm) 10% 129.220% 151.2 30% 166.3 40% 179.7 50% 193.1 60% 208.8 70% 230.0 80% 259.490% 304.0 95% 343.0

TABLE 2B Particle Size Distribution for Eutectic Metal AlloyNanoparticles with Tetraethylenepentamine Size (nm) % Channel % Pass6,540 0.0 100 5,500 0.0 100 4,620 0.0 100 3,890 0.0 100 3,270 0.0 1002,750 0.0 100 2,312 0.0 100 1,944 0.0 100 1,635 0.84 100 1,375 0.0 99.161,156 0.04 99.16 972 0.56 99.12 818 0.47 98.56 687 0.0 98.09 578 0.098.09 486 0.22 98.09 409 2.80 97.87 344 7.90 95.07 289 12.28 87.17 24317.35 74.89 204.4 23.47 57.54 171.9 17.83 34.07 144.5 8.55 16.24 121.54.36 7.69 102.2 2.72 3.33 85.9 0.61 0.61 72.3 0.0 0.0 60.8 0.0 0.0 51.10.0 0.0 43.0 0.0 0.0 36.1 0.0 0.0

Rheology.

The rheology of the conductive adhesive composition prepared in Example1B was measured. The composition had an average shear viscosity (40-400s⁻¹) of 7.0 cps. The viscosity measurements are shown below in Table 3.An ARES-G2 Rheometer was used to measure the viscosity.

TABLE 3 Viscosity of Conductive Adhesive Composition Shear Rate Range(s⁻¹) 4-400 10-400 40-400 1-6.3 Shear Index 0.94 0.96 0.99 0.97 MeanViscosity 6.85 6.92 7.00 6.42 s viscosity 0.20 0.15 0.08 0.06 CVviscosity 2.9 2.2 1.1 0.9

Surface Tension.

Surface tension was measured to be 32 mN/m using a K100 ForceTensiometer by Krüss.

Printing of Conductive Adhesive Composition.

The conductive adhesive composition was jetted using an Optomec AerosolJet System in Pneumatic Aerosol mode (PA). A 300 μm nozzle was used witha 3 mm offset distance between the nozzle and the substrate. Theprinting rate was maintained at 10 mm/s. The following gas flowparameters were used to print the conductive adhesive composition:Sheath Gas=40 cm³/min, Atomization Gas=650 cm³/min, Exhaust gas=650cm³/min. The conductive adhesive composition was jetted onto flexiblepolycarbonate and rigid polycarbonate substrates.

Resistance Test Measurements.

A test pattern was printed with silver nanoparticle ink onpolycarbonate. There were two lines each terminated in a pad. Betweenthe two pads was a 5 mm gap. The conductive adhesive composition wastested in two ways. In the first test, the conductive adhesivecomposition was printed only on the pads (and not in the gap) (see FIG.1A), the substrate was heated to about 65° C., and a resistor was placedacross the gap of the silver printed pads (see FIG. 1B), applyingpressure to the resistor to make the Field's metal particles flow (seeFIG. 1C). The conductive adhesive composition was cured at 120° C. for 2hours.

In the second test, the conductive adhesive composition was printed onthe pads and across the gap (see FIG. 2A), the substrate was heated toabout 65° C., and a resistor was placed across the gap of the silverprinted pads, applying pressure to the resistor to make the Field'smetal particles flow (see FIG. 2B). The conductive adhesive compositionwas cured at 120° C. for 2 hours.

For both tests, the gap was spanned by a surface mount 100Ω resistor.The conductive adhesive was evaluated by measuring the resistance acrossthe two silver lines. The leads of the digital multimeter were placed oneither side of the gap on the conductive silver lines. The adhesive isdeemed sufficiently conductive if the measured resistance is 100Ω,indicating that the conductive adhesive is not contributing additionalresistance. When the conductive adhesive was printed on the silver padsand across the gap between the pads, the multimeter measured 101.3Ω,indicating that the conductive adhesive does not significantlycontribute additional resistance to the “circuitry” (1%). When theconductive adhesive was printed on the silver pads only and 1Ω resistorswere used to bridge the gap between the pads, the multimeter measuredabout 1.5Ω, indicating that the conductive adhesive does notsignificantly contribute additional resistance to the “circuitry.” Whilenot wishing to be bound by theory, it is hypothesized that the extra1.3Ω or 0.5Ω could be from resistance in the silver lines, the contactresistance between the probes and the silver lines, from the conductiveadhesive, or a combination of these possibilities. Given that aresistance was measured indicates that the adhesive was functioninganisotropically, since there is no shorting across the gap (i.e., thereis not a conductive pathway in the region between the gap even thoughthere was adhesive.

Adhesion Test.

Adhesion was assessed qualitatively using several steps in attempts toremove the resistor from the silver pads, in increasing amounts ofapplied force. First, the polycarbonate plaque was turned over. Second,the back of the plaque was tapped with the three fingers. Third, theplaque was turned on its side and the tapped on a table. Finally, forcewas applied to the resister using tweezers to pop it off. The curedconductive adhesive composition required applied force (i.e., the use oftweezers) to remove the resistor from the silver pads. The resistor wasnot removed by merely turning the plaque over, tapping the back of theplaque with fingers, or tapping the plaque on a table. This demonstratesthat the cured conductive adhesive composition had adequate adhesion.

What is claimed is:
 1. A conductive adhesive composition comprising: atleast one epoxy resin; at least one polymer chosen from polyvinylphenols and polyvinyl butyrals; at least one melamine resin; a pluralityof eutectic metal alloy nanoparticles; and at least one solvent.
 2. Theconductive adhesive composition of claim 1, wherein the plurality ofeutectic metal alloy nanoparticles comprise Field's metal.
 3. Theconductive adhesive composition of claim 1, wherein the plurality ofeutectic metal alloy nanoparticles further comprise at least oneorganoamine stabilizer selected from the group consisting of butylamine,octylamine, 3-methoxypropylamine, pentaethylenehexamine,2,2-(ethylenedioxy)diethylamine, tetraethylenepentamine,triethylenetetramine, and diethylenetriamine.
 4. The conductive adhesivecomposition of claim 1, having a solids content ranging from about 20%to about 80%, based on a total weight of the conductive adhesivecomposition.
 5. The conductive adhesive composition of claim 1, whereinat least one solvent is selected from the group consisting of propyleneglycol methyl ether acetate, di(propylene glycol) methyl ether acetate,(propylene glycol)methyl ether, di(propylene glycol)methyl ether, methylisobutyl ketone, diisobutyl ketone, and 1-phenoxy-2-propanol.
 6. Theconductive adhesive composition of claim 1, wherein the at least onemelamine resin is selected from the group consisting of a methylatedpoly(melamine-co-formaldehyde), butylatedpoly(melamine-co-formaldehyde), isobutylatedpoly(melamine-co-formaldehyde), acrylatedpoly(melamine-co-formaldehyde), and methylated/butylatedpoly(melamine-co-formaldehyde).
 7. The conductive adhesive compositionof claim 1, wherein the composition has a viscosity ranging from about 2cps to less than about 300 cps at a temperature of about 20° C. to about30° C.
 8. The conductive adhesive composition of claim 1, wherein the atleast one epoxy resin is selected from the group consisting of bisphenolA diglycidyl ether, bisphenol A propoxylate diglycidyl ether, glycidylepoxy resins, trimethylolpropane triglycidyl ether, neopentyl glycoldiglycidyl ether, poly(propylene glycol) diglycidyl ether,tris-(hydroxyl phenyl)-methane-based epoxy resins, and cycloaliphaticepoxides.
 9. The conductive adhesive composition of claim 1, furthercomprising at least one adhesion promoter.
 10. The conductive adhesivecomposition of claim 1, wherein the at least one polymer is a polyvinylphenol selected from the group consisting of poly(4-vinylphenol),poly-p-vinylphenol, poly(vinylphenol)/poly(methyl acrylate),poly(vinylphenol)/poly(methyl methacrylate), andpoly(4-vinylphenol)/poly(vinyl methyl ketone).
 11. The conductiveadhesive composition of claim 1, wherein the conductive adhesivecomposition is jettable by inkjet or aerosol jet printing.
 12. Anelectronic device comprising: a substrate; conductive features disposedon the substrate; a conductive electrical component disposed over theconductive features; and a conductive adhesive composition disposedbetween the conductive features and the conductive electrical component,wherein the conductive adhesive composition comprises at least one epoxyresin, at least one polymer chosen from polyvinyl phenols and polyvinylbutyrals, at least one melamine resin, and a plurality of eutectic metalalloy nanoparticles.
 13. The electronic device of claim 12, wherein thesubstrate is selected from the group consisting of silicon, glass,plastics, sheets, fabrics, synthetic papers, and mixtures thereof. 14.The electronic device of claim 12, wherein the substrate is selectedfrom the group consisting of polyester, polycarbonate, polyimide sheets,polyethylene terephthalate sheets, polyethylene naphthalate sheets, andmixtures thereof.
 15. The electronic device of claim 12, wherein theconductive features comprise an electrically conductive element formedfrom a metal nanoparticle conductive ink composition.
 16. The electronicdevice of claim 15, wherein the metal nanoparticle conductive inkcomposition is a silver nanoparticle conductive ink composition.
 17. Theelectronic device of claim 12, wherein the conductive adhesivecomposition has a viscosity ranging from about 2 cps to about 300 cps ata temperature of about 20° C. to about 30° C.
 18. A method of making aconductive adhesive composition comprising: mixing at least one epoxyresin, at least one polymer chosen from polyvinyl phenols and polyvinylbutyrals; at least one melamine resin; and at least one solvent tocreate a mixture; and adding a plurality of eutectic metal alloynanoparticles to the mixture to create a conductive adhesivecomposition.
 19. The method of claim 18, wherein the plurality ofeutectic metal alloy nanoparticles comprise a Field's metal alloy. 20.The method of claim 18, wherein the conductive adhesive composition hasa solids content ranging from about 20% to about 80%, based on a totalweight of the conductive adhesive composition.